There has always been a problem with exterior doors and preventing moisture from being blown under and around exterior doors.
The above is particularly true where porches or other structures are lacking. Also, in open areas even with porches or other covering structure, rain can be driven almost horizontally against the entry door. This is particularly true in coastal areas where storms are quite often accompanied by very strong winds.
The result of water ingressing under the entry doors not only causes the adjacent interior floor to become wet, but over a period of time can cause the flooring to rot as well as the floor joist and door jamb. When this happens, very expensive repairs must be made. Once this is accomplished and a new door installed, the process starts all over with the floor becoming wet and rot setting in.
Specially extruded and molded thresholds with special weather seal systems have been devised in an effort to prevent the ingress of undesired water under and around entry doors. Even pan-like means have been suggested as a possible solution to the problem. Because of the details of these various means, none have proved to be successful in preventing strong, wind driven rain from being blown under the entry doors thus allowing the ingress of undesirable moisture into the interior of the structure.